Exploration forges differences in identical twins

Distinctive personalities in mice related to brain development

Genetically identical mice that thoroughly explored a complex cage grew more neurons (shown in black on right) in a key brain region than did mice that explored less (left), new research finds. The findings may shed light on how distinctive personalities arise even in identical twins raised in the same environment.

Identical twin mice sharing the same mazelike environment develop distinct personalities based on how much they explore their surroundings, researchers report in the May 10 Science. After death, those differences were reflected in the animals’ brains.

The study “highlights something for which we had some intuition before, but actually quantifies it,” says Fred Gage, a neuroscientist at the Salk Institute for Biological Studies in La Jolla, Calif.

Some character and biological differences between identical twins may originate as early as pregnancy. But twins become more and more different as life goes on, even when they grow up together. Scientists have recognized that having distinct experiences within the same environment might boost such personality differences, but that’s difficult to test in humans.

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